This invention relates generally to the field of magnetic data storage devices, and more particularly, but not by way of limitation, to improving disc drive operational performance by adaptively attenuating the effects of vibrational inputs which are simultaneously applied to a disc drive along multiple axes.
Disc drives are used as primary data storage devices in modern computer systems. A typical disc drive includes one or more axially aligned discs that are rotated at a high speed by a spindle motor. A corresponding array of read/write transducing heads are supported adjacent the discs and used to transfer data between the discs and a host computer in which the disc drive is mounted.
Each disc surface is provided with prerecorded servo data arranged as a plurality of servo fields which are written during disc drive manufacturing. The servo data define a plurality of concentric tracks on each surface and are decoded to provide head position and velocity information to a servo control circuit configured to controllably position the heads adjacent the tracks. Each track further includes a plurality of user data fields, or sectors, to which user data are written and from which user data are subsequently read by the heads. All of the tracks on each of the disc surfaces at a given radius collectively make up a cylinder.
During a track following mode in which a selected head is maintained over a corresponding track, the servo control circuit transduces the servo data to determine the actual position of the head relative to the track and generates a position error signal (PES) indicative of the difference between the actual position and a desired position (such as over the center of the track). In response to the magnitude of the PES, the servo control circuit provides a current command signal to a power amplifier which applies current to an actuator motor, such as a voice coil motor (VCM), to adjust the position of the head to remove the position error.
There exists a continued demand in the marketplace for drives with ever higher data capacities, at lower cost. Disc drive manufacturers have responded by providing successive generations of drives with higher data storage areal densities (i.e., the amount of data stored per unit area), resulting in significant annual increases in data track densities (greater than 60% per year in recent years). As individual tracks become narrower and closer together, greater demands are placed on servo control circuits to maintain the heads over the tracks during track following modes of operation, especially in the presence of external vibrations. Such vibrations can be generated through the operation of adjacent drives, such as in a multi-drive array, and transmitted from drive to drive through chassis mounts used to secure the drives within the array.
Vibrational components are typically characterized as translational, or rotational. Translational vibrations tend to move a disc drive housing back and forth along a selected axis parallel to the discs, whereas rotational vibrations tend to rotate a disc drive housing about an axis parallel to the axis of disc rotation. Translational vibrations will generally have a smaller effect upon the ability of the servo control circuit to maintain the heads at a selected position with respect to the discs, as the discs and the actuator will both respond to the movement induced by such translational vibrations. Particularly, disc drive designers typically attempt to provide balanced actuators to minimize actuator rotation during a translational vibration disturbance.
However, such is not true with rotational vibrations. Even with a nominally balanced actuator, rotational vibrations will tend to move the discs relative to the actuator because the actuator, acting as a free body, remains essentially undisturbed due to inertial effects while the discs, mounted to the housing, are displaced by imparted rotational vibration. When sufficiently severe, such movement will cause an xe2x80x9coff-trackxe2x80x9d condition whereby a head is moved away from a selected track being followed. Such off-track conditions can adversely affect the ability of the drive to transfer data between the discs and host device.
The problems associated with rotational vibration are well known in the disc drive art. Compensation attempts have included use of sensors that can detect the presence of rotational vibration in a disc drive, such as discussed in U.S. Pat. No. 5,235,472 issued to Smith, assigned to the assignee of the present invention. Efforts to both detect and compensate rotational vibration using feedforward control include U.S. Pat. No. 5,663,847 issued to Abramovitch; White and Tomizuka, Increased Disturbance Rejection in Magnetic Disk Drives by Acceleration Feedforward Control, 13th Triennial World Congress, San Francisco, U.S.A., 1996; and Pannu and Horowitz, Increased Disturbance Rejection for Hard Disc Drives using Accelerometers, Computer Mechanics Laboratory, Department of Mechanical Engineering, University of Berkeley, Calif., 1998.
While operative, these and other references are generally directed to detecting and compensating external vibrations along one-dimension at a time. In practice, induced vibration is seldom purely rotational or translational along one axis, but rather is presented as a composite disturbance along multiple axes. Hence, there is a continued need in the art for an improved approach to attenuating the effects of external vibration along multiple axes, and it is to such improvements that the present invention is directed.
The present invention is directed to an apparatus and method for improving disc drive operational performance by attenuating effects of externally generated vibration applied along multiple axes of a disc drive.
In accordance with preferred embodiments, the disc drive includes a base deck, a rotatable disc supported by the base deck with a recording surface on which a plurality of concentric data tracks are defined, and a read/write head which accesses the data tracks. An actuator motor controllably moves the head relative to the recording surface, and a servo circuit generates a position error signal indicative of head position error in relation to detected head position and desired head position.
In accordance with a preferred embodiment, the servo circuit is configured to determine a plant estimate indicative of transfer function response of the disc drive while the disc drive is operated off-line. The disc drive is further provided with a sensor network having a plurality of vibration sensors, each vibration sensor configured to generate an acceleration signal aligned along different disc drive axes, indicative of a different component of the externally generated vibration applied along the corresponding axis of the disc drive.
An adaptive filter network has a plurality of filters arranged in parallel, each filter adaptively filtering a selected one of the acceleration signals to generate a filtered acceleration signal. The adaptive filter network combines the filtered acceleration signal to generate a compensation signal which is used by the servo circuit to reduce head position error induced by the externally generated vibration. Each adaptive filter is preferably characterized as an adaptive multi-tap finite response filter (FIR) having tap weights selected in response to the plant estimate and the externally generated vibration.
These and other features and advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.